Heterobimetallic Complexes Bridged by Imidazol{[4,5-f][1,10]-phenanthrolin}-2-ylidene: Synthesis and Catalytic Activity in Tandem Reactions

A series of monometallic complexes obtained by metalation of the phenanthrolin donor in 1,3-dibutyl-1H-imidazol[4,5-f][1,10]phenanthrolin}ium hexafluorophospate 1 (M = Pd 2, Ru 3, Ir 4) have been prepared. Subsequently, the imidazolium moiety of complexes 2–4 was metalated with M′, leading to the heterobimetallic phenanthroline/NHC complexes (M/M′ = Pd/Rh 5, Pd/Ir 6, Pd/Ru 7, Ru/Pd 8, Ir/Pd 9) and the homobimetallic complex (M/M′ = Ir/Ir 10). The new complexes were characterized by elemental analysis, FTIR, UV–vis, and NMR spectroscopy. The molecular structures of the heterobimetallic complexes 5 and 6 were determined by X-ray diffraction studies. The catalytic activity of the heterobimetallic complexes 5–9 were tested in selected tandem reactions (dehalogenation/transfer hydrogenation and Suzuki–Miyaura coupling/transfer hydrogenation). It was found that the M/M′ heterobimetallic complexes display higher catalytic activities when compared to equimolar mixtures of the mononuclear complexes M and M′, thus ...